This invention relates generally to femoral prostheses and methods for their implantation.
Total hip replacement became a clinical reality for the first time in November, 1962. The femoral head and neck were removed, the upper marrow canal of the femur was cleaned out (i.e., marrow contents removed), and the metal femoral component was inserted into the femur. Total hip replacement using a femoral component or implant is generally successful for the short term (ten years), however in the long run, deterioration of the bone occurs and the implant may loosen.
Bone deterioration adjacent femoral implants is a multi-factored process which includes at least two elements, strain deprivation and osteolysis. Bone loss due to strain deprivation (or what is commonly but incorrectly referred to as xe2x80x9cstress shieldingxe2x80x9d) occurs in association with substantially all conventional intramedullary femoral components and is caused by the implant splinting the upper femur, preventing the upper femur from being subjected to natural bending. My prior application, PCT Application Serial No. US97/14233, includes features directed to alleviating splinting. Osteolysis is a late complication of joint replacement surgery in which the bone adjacent the implant develops lesions, either xe2x80x9cscooped outxe2x80x9d (focal) or diffuse (linear) areas. Osteolysis is somewhat less common than bone loss due to strain deprivation, and depends on the type of implant used. Several factors are known to contribute to osteolysis, including access of joint wear debris to a joint space JS above the collar of the component and to the area between the implant and the bone (the implant-bone interface IB). Joint wear debris carried by the fluid remains in the joint space JS and becomes concentrated. The synovial lining of the joint has limited ability to absorb and encapsulate the wear debris, resulting in osteolysis of the exposed bone. Another factor is joint fluid pressure in the implant-bone interface IB. The latter factor commonly occurs in prior art implants because fluid is able to enter the implant-bone interface IB. As the person walks, high fluid pressures are generated at the interface and within the bone cells. Recent research suggests that joint fluid pressure is a significant factor in osteolysis.
Although much less common than strain deprivation or osteolysis, the most disastrous cause of bone deterioration adjacent a femoral implant is infection. Infection may occur shortly after the total hip replacement operation (acute infection), or may occur months or years after the operation (late infection). Acute infections may be caused by bacterial contamination of the incision by airborne bacteria or from bacteria from the patient""s skin. Late infections usually are caused by bacteria going through the patient""s circulatory system and lodging in the bone adjacent the femoral implant.
Infection adjacent a femoral implant is a serious problem because of the pain, fever and disability it causes. The bacteria (or other organisms) cause infection in the bone and soft tissues around the implant and begin to multiply (osteomyelitis). The body""s attempt to fight the infection tends to damage the bone as well.
The diagnosis of deep infection of a total joint replacement is often delayed because of the inaccessibility of the hip joint within the body. The diagnosis of infection of a total hip replacement requires aspiration of joint fluid (inserting a needle into the joint space JS (FIG. 34) and drawing infected fluid out of the joint with a syringe) or alternatively, obtaining deep tissue specimens from the joint. Tissue specimens are obtained by open surgery at the joint, or, much less commonly, by arthroscopic surgery (exploration of the joint through small incisions using fiberoptic telescopes).
An infection may be present at the implant-bone interface IB and not manifest itself in the joint fluid (false negative aspiration). It can be technically difficult to obtain fluid from the hip joint because of scarring from the previous surgery. The scar tissue which forms around a femoral implant may also make arthroscopic visualization of the joint difficult. Surgically exposing the hip to obtain tissue samples carries with it the pain and disability of open surgery as well as the risk of introducing bacteria around the implants.
Infrequently, the infection can be treated without removing the implant. The hip joint is surgically exposed and cleaned (debrided) through removal of dead and infected tissue. However, it is not possible to clean everywhere around the implant. Moreover, the interface between the bone and implant is generally inaccessible, which inhibits the introduction of antibiotics into the implant-bone interface IB. As shown in FIG. 34, antibiotics introduced into the joint space JS will generally remain in the joint space and will not flow down into the implant-bone interface IB. Intravenous systemic antibiotics are administered for several weeks or months following surgery. This method of treating an infection adjacent an implant usually is attempted only on early infections (less than three or four weeks) and is not always successful in eradicating the infection.
More commonly, infection adjacent a femoral prostheses requires complete removal of the implant and removal of bone cement (if present). The removal of cemented or non-cemented intramedullary stem femoral implants will destroy some amount of bone. In the case of removal of porous ingrowth (non-cemented) femoral implants, the destruction of bone is extensive. These components frequently require cutting the upper thigh bone (femur) in half longitudinally (extended trochanteric osteotomy), cutting the metal stem in half transversely, and using a hollow coring drill to remove the lower half of the stem (trephining). The extent of bone loss associated with removal of total hip replacement femoral implants is aggravated in cases where pre-existing bone loss from strain deprivation and osteolysis is present. Once the implant is removed, the patient is given systemic (intravenous or oral) antibiotics for two months or more. When there is evidence that the infection has been cleared, a new total hip replacement is installed in a second operation. Fixation of the new implant in the bone is frequently compromised by loss of bone stock.
In some patients, the joint replacement implants are permanently left out (Girdlestone procedure). This option is considered for patients having a weakened immune system, such as those with diabetes, rheumatoid arthritis or who require steroids. A Girdlestone procedure is also considered for patients who are too ill to withstand an additional major operation. With the hip implant absent, the hip joint tissues contract and the leg becomes significantly shorter. With no bony or mechanical connection or support, the hip is unstable and frequently painful. Most patients require the use of crutches, walker or wheelchair after a Girdlestone procedure.
Another problem in the treatment of infection is presented by the systemic administration of antibiotics, taken orally or intraveneously. Systemic antibiotics expose the entire body to the antibiotic. Potential side effects of antibiotics limit the amount that can be given. Side effects of systemic antibiotics include allergic reactions, impairment of kidney function, damage to the nerves which allow hearing and balance, gastrointestinal complications, and other problems. Additionally, bone has a relatively poor blood supply compared with other tissues, e.g., muscles or internal organs, so that achieving high enough concentrations of antibodies in the bone to eradicate the bacterial infection is difficult. The implant, acrylic bone cement (if present), nonviable bone and scar tissue may also harbor deep seated bacteria which may again begin to multiply once antibiotics are discontinued.
An alternative method of delivering antibiotics to an infected hip implant employs an antibiotic cement spacer. The infected hip replacement components are removed and the bone is thoroughly cleaned of infected tissue. A sterilized stem of a femoral implant is covered with a layer of acrylic cement which contains high concentrations of an antibiotic. The stem/antibiotic cement composite structure is placed in the marrow canal of the femur. One advantage of this method is the delivery of high local concentrations of antibiotic directly to the infected tissues. This may decrease the need for systemic antibiotics with their potential side effects. Another advantage is the maintenance of the soft tissue length about the hip which makes the later implantation of a new hip implant technically easier. One disadvantage of the antibiotic cement spacer is a significant decline in the antibiotic levels in the fluid and tissues about the hip after two or three weeks. Also, the antibiotic spacer is usually put in loosely to facilitate later removal. The resulting instability of the implant within the bone may cause pain and prevent full weight bearing. Moreover, if a spacer is left in for a long time it may be difficult to remove, which may result in additional bone loss upon removal.
A second method of delivering antibiotics directly to the infected tissues about an infected hip implant site is the infusion port method. This technique is used after removal of an infected implant to provide a renewable supply of antibiotics directly to the infection site. The port method involves placing an infusion port under the skin away from the infected joint at a location where it is readily accessible from outside the body. The infusion port is anchored with sutures to fascia (connective tissue). A length of tubing from the port is passed under the skin to the site of infection (e.g., hip, knee, shoulder). After surgically cleaning the joint and removal of the infected implants, the end of the tubing is placed in the infected joint. After the operation to insert the infusion port, a needle is passed through the skin overlying the port, through a plastic, self-sealing membrane of the port and into the port. A syringe attached to the needle contains a solution of antibiotics that is infused through the port and tubing directly into the joint. The advantage of this method over an antibiotic spacer technique is that antibiotics can be administered daily, or more often if necessary. This renewable source of antibiotics provides extremely high local concentrations of antibiotics directly to the site of the infection without the side effects associated with systemic antibiotics. These concentrations can be maintained indefinitely by repeatedly infusing antibiotics directly into the joint. A disadvantage of the infusion port method is that it usually is combined with removal of the implant to assure that the antibiotic has access to all of the potentially infected sites at the joint. Referring again to FIG. 34, when conventional intramedullary stem femoral implants are left in place, the antibiotics may not be able to reach the interface between the bone and the implant (or between the cement and the bone).
Among the several objects and features of the present invention may be noted the provision of a prosthesis and method of implantation which inhibit bone deterioration; the provision of such a prosthesis and method which reduces fluid pressure in the implant-bone interface; the provision of such a prosthesis and method which transports joint wear debris away from the joint space; and the provision of such a prosthesis which has a longer useful life.
Further objects of the invention include the provision of a method and apparatus for diagnosing and treating infections associated with a prosthesis which does not require removal of the prosthesis; the provision of such a method and apparatus which achieves high antibiotic levels at the infection site without affecting the entire system of the patient; and the provision of such a method that maintains soft tissue length adjacent the prosthesis.
Generally, a bone prosthesis for implantation at a joint comprises a stem sized and shaped for implantation in a bone at the joint such that at least a portion of the stem is received in the bone and a portion is exposed to locations outside the bone. The stem has a passageway arranged to vent fluid from a first location which is subject to elevated fluid pressures when the joint is in use after implantation of the prosthesis to a second location for venting fluid pressure from the first location to the second location thereby to inhibit fluid pressure build up between bone located at the joint and the prosthesis.
In another aspect of the invention, a bone prosthesis for implantation at a joint includes a stem having a tip generally at one end thereof. The stem is sized and shaped for reception in a bone at the joint such that the tip of the stem is exposed to locations outside of the bone. The stem has a passageway extending from a first location on the bone prosthesis to a second location on the bone prosthesis.
Another aspect of the present invention is a method for implanting a femoral head-neck prosthesis in a femur without the use of cement. The femur has a shaft and a neck at the upper end of the shaft at the medial side of the femur. The prosthesis has a longitudinal passageway for venting fluid pressure from a first location which is subject to elevated fluid pressures when the joint is in use after implantation of the prosthesis to a second location for venting fluid pressure from the first location to the second location thereby to inhibit fluid pressure build up between bone located at the joint and the prosthesis. The method comprises the steps of cutting the neck of the femur to form a seat on the femur neck, drilling a passage along a line through the shaft of the femur and inserting the stem of the prosthesis in the passage of the femur such that the longitudinal passageway for venting fluid pressure is not occluded.
Yet another aspect of the invention is a method of minimally invasively accessing the femoral head-neck prosthesis which is transosseously implanted in a femur in a thigh of a patient. The prosthesis includes a stem having a passageway extending at least partway through the stem along a longitudinal axis and opening at a tip of the stem. The passageway is in fluid communication with a prosthesis-bone interface. The stem is implanted such that the opening of the passageway in the stem is accessible from a location external to the femur. The method includes examining the prosthesis using an X-ray device while simultaneously rotating the femur until a viewing plane of the X-ray device is generally parallel with the longitudinal axis of the passageway. An intersection point of the longitudinal axis of the stem with skin of the thigh is determined. An incision is made at the intersection point and an instrument is inserted through the skin generally along the longitudinal axis and into the opening of the passageway.
Other objects and features of the present invention will be in part apparent and in part pointed out hereinafter.